The present invention relates to ionic liquids and methods for their preparation. In particular, the present invention relates to ionic liquids that are liquid at relatively low temperatures. Ionic liquid compounds according to the present invention are liquid at temperatures below about 100° C., and are preferably liquid below about 60° C., and more preferably are liquid at or near ambient temperature. The present invention further relates to polymeric ionic electrolytes and methods for their preparation. In particular, the present invention relates to gelling the ionic liquids of the present invention by adding certain polymers. Polymeric compounds according to the present invention are gel-like at temperatures between about 0° and about 200° C., and have conductivities of greater than 5 millisiemens/cm at or near ambient temperature.
There is currently great interest in the use of ionic liquids as solvents for a wide range of applications. Ionic liquids are low melting point salts that, being composed entirely of ions, posses negligible vapor pressures. By carefully choosing among a wide range of possible cations and anions, ionic liquids may be prepared that are liquid at low temperatures. A number of other solvent properties can be controlled as well, such as polarity and other factors that determine a liquid's suitability as a solvent for a given end-use application.
Conventional organic solvents are high on the list of hazardous chemicals because they are typically volatile liquids that are used in large quantity and produce harmful vapors that are difficult to contain. Ionic liquids, on the other hand, are non-volatile, non-flammable and highly stable solvents, and as such are rapidly emerging as promising replacements for the traditional volatile organic solvents.
Not only do ionic liquids have utility as industrial solvents, they are also suitable, for example, as highly polar solvents for use in preparative chemistry, and as catalysts. The negligible vapor pressure of ionic liquids facilitates product separation by fractional distillation. They also have particular application in electrochemistry, for example, in batteries, fuel cells, and photovoltaic devices and in electrodeposition processes.
International Application No. PCT/GB00/01090 discloses ionic liquids that are specific quaternary ammonium salts of zinc, tin and iron halides. The disclosed ionic liquids are reportedly liquid below 60° C. and inexpensive to produce. The quaternary ammonium salts of zinc and tin, and iron halides, are reportedly less water sensitive that earlier prior art ionic liquids, which were quaternary ammonium salts of aluminum trichloride.
Hagiwara et al., J. Fluorine Chem. 99, 1 (1999), and J. Electrochem. Soc., 149, D1 (2002), have recently disclosed several ionic liquids comprising various imidazolium fluorides combined with hydrogen fluoride at a specific mole ratio of 1:2.3. Otherwise, prior art salts are minimally electrically conductive, and all are viscous liquids. There remains a need for ionic liquids with greater fluidity for solvent applications and with an electrical conductivity better suited for electrochemical applications.
There is also currently great interest in the use of polymeric gels as electrolytes for a wide range of applications. Polymeric gels are low volatility, highly viscous materials that, being composed almost entirely of polymers, posses negligible vapor pressures.
Conventional electrolytes are high on the list of hazardous chemicals because they are typically volatile liquids that are used in large quantity and produce harmful spills that are difficult to contain in consumer applications. Ionic gels, on the other hand, are non-volatile, non-flammable and highly stable materials, and as such are rapidly emerging as promising replacements for the traditional liquid electrolytes. They also have particular application in electrochemistry, for example, in super capacitors, batteries, fuel cells, and photovoltaic devices and in electrodeposition processes.
Yoshida et al., Sci. Tech. J., 38, 39-45 (June 2002) disclosed polymeric electrolyte gels formed by adding cellulosic materials and a cross-linking reagent to an electrolyte solution of LiBF4 in a mixture of ethylene carbonate and diethyl carbonate. The disclosure shows that the conductivities of these gels are less than 3 milli-siemens/cm. There is thus also a need for polymeric gels with higher electrical conductivities.